The genetic controls and molecular mechanisms of the steroid hormone ecdysone, and of as yet unidentified hormones that appear to control sexual dimorphism, will be studied in Drosophila. The ecdysone experiments involve a temperature-sensitive ecdysoneless mutant recently isolated, which has revealed the times and locations of ecdysone action during development. We plan to isolate other ecdysone defective mutants, including mutants incapable of responding to ecdysone. The long term goals are to identify proteins and mRNAs that are induced by ecdysone, the cellular components to which ecdysone binds, and the presumed chromosomal binding sites. The possible existence of sex hormones in Drosophila is suggested by our studies of the doublesex region of the 3rd-chromosome which controls the development of all sexually dimorphic tissues, including the gonads and the internal and external genitalia. This region contains two functional units, one specific for genetic males and the other for genetic females, which are coordinately regulated. The results of gonad transportation tests suggest that the doublesex defect is nonautonomous and therefore could involve hormone action. Further genetic and biochemical experiments are planned to elucidate the function of the doublesex region.